Gantt Chart

Also Called: milestones chart, project bar chart, activity chart.

A Gantt chart is a bar chart that shows the tasks of a project, when each must take place and how long each will take. As the project progresses, bars are shaded to show which tasks have been completed. People assigned to each task also can be represented.

When to Use Gantt Charts

When scheduling and monitoring tasks within a project.

When communicating plans or status of a project.

When the steps of the project or process, their sequence and their duration are known.

When it’s not necessary to show which tasks depend on completion of previous tasks.

Gantt Chart Basic Procedure

Construction

Identify tasks:

Identify the tasks needed to complete the project.

Identify key milestones in the project by brainstorming a list, or by drawing a flowchart, storyboard or arrow diagram for the project.

Identify the time required for each task.

Identify the sequence: Which tasks must be finished before a following task can begin, and which can happen simultaneously? Which tasks must be completed before each milestone?

Draw a horizontal time axis along the top or bottom of a page. Mark it off in an appropriate scale for the length of the tasks (days or weeks).

Down the left side of the page, write each task and milestone of the project in order. For events that happen at a point in time (such as a presentation), draw a diamond under the time the event must happen. For activities that occur over a period of time (such as developing a plan or holding a series of interviews), draw a bar that spans the appropriate times on the timeline: Align the left end of the bar with the time the activity begins, and align the right end with the time the activity concludes. Draw just the outlines of the bars and diamonds; don’t fill them in.

Check that every task of the project is on the chart.

Using the Chart

As events and activities take place, fill in the diamonds and bars to show completion. For tasks in progress, estimate how far along you are and fill in that much of the bar.

Place a vertical marker to show where you are on the timeline. If the chart is posted on the wall, for example, an easy way to show the current time is with a heavy dark string hung vertically across the chart with two thumbtacks.

Gantt Chart Example

The figure below shows a Gantt chart used to plan a benchmarking study. Twelve weeks are indicated on the timeline. There are two milestone events, presentations of plans for the project and for the new process developed in the study. The rest of the tasks are activities that stretch over periods of time.

Gantt Chart Example

The chart shows the status at Thursday of the sixth week. The team has finished seven tasks through identifying key practices, measures and documentation.

This is a hectic time on the project, with three time-consuming activities that must happen simultaneously:

The team estimates it is one-fourth finished with identifying benchmark partners and scheduling visits; one-fourth of that bar is filled.

Team members have not yet begun to identify the current state.

They are halfway through collecting public data, which puts them slightly ahead of schedule for that task.

They are behind schedule for the first two of these tasks and ahead of schedule for the third. Perhaps they need to reallocate their workforce to be able to cover the three activities simultaneously.

There is a fourth activity that could be happening now (develop benchmark questions), but it is not urgent yet. Eventually the team will have to allocate resources to cover it too, before visits can begin.

Gantt Chart Considerations

Sometimes Gantt charts are drawn with additional columns showing details such as the amount of time the task is expected to take, resources or skill level needed or person responsible.

Beware of identifying reviews or approvals as events unless they really will take place at a specific time, such as a meeting. Reviews and approvals often can take days or weeks.

The process of constructing the Gantt chart forces group members to think clearly about what must be done to accomplish their goal. Keeping the chart updated as the project proceeds helps manage the project and head off schedule problems.

It can be useful to indicate the critical points on the chart with bold or colored outlines of the bars.

Computer software can simplify constructing and updating a Gantt chart.

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